ASSESSMENT OF SOIL RADIOACTIVITY AND HEAVY METAL CONTENT OF SOME GOLD MINE PITS IN OSUN STATE, NIGERIA.

Abstract

In this work, a total of forty five soil samples were taken from gold mining sites and non-mining environment within Epe, Osun State. Forty soil samples were collected from ten mining pits at four different locations and five soil samples were collected from a non-mining environment within the study area as background samples. The concentrations of natural radionuclides and heavy metals in the samples were assessed using High Purity Germanium (HPGe) detector and Atomic Absorption Spectrometer. The results revealed that the activity concentrations of 40K exhibited the highest activity concentrations in all studied pits in the study area. The radiological hazard to humans due to the radiation emitted from natural radionuclides in soils collected from the areas studied was assessed. The concentrations of heavy metals measured were used in assessing the level of pollution and health risks due to exposure to heavy metals in the soil. The statistical analysis of the results was carried out using SPSS software to determine the relationship between radionuclides and heavy metals in the soil. The mean activity concentrations of 226Ra, 232Th and 40K were 6.03 ± 1.23 Bq kg-1, 8.52 ± 1.25 Bq kg-1 and 216.18 ± 28.70 Bq kg-1 respectively and were found to be lower than the world average values of 35, 30 and 400 Bq kg-1 for 226Ra, 232Th and 40K respectively. The values of the radiation hazard indices in all locations are below the recommended maximum permissible limit set by the International Commission on Radiological Protection (ICRP). The mean values for heavy metal concentrations were 20.13 mg kg-1 for Cr, 14.18 mg kg-1 for Cu, 11.05 mg kg-1 for Pb and 18.18 mg kg-1 for Zn. These values are lower than the world standard values of 67, 24, 20 and 67 mg kg-1 for Cr, Cu, Pb and Zn respectively. The results of pollution indices showed none to medium contamination factor (CF), low to moderate contamination degree (Cd) and the mean of pollution load index (PLI) to be less than unity. The Cd and PLI values showed similar trends at various sampling pits. The values of non-carcinogenic risk for the heavy metals were generally less than 1. The carcinogenic risk of Pb is less than the acceptable limit of 1E-06 while Cr and total risk exceed this limit. The result from cluster and correlation analysis showed that heavy metals are not responsible for increasing radioactivity level in the soil of the study area.